The characteristics and catalytic performance of nanocr ystalline and no n - nano crystalline ZSM - 5 Zeolites were studied. The zeolites were characterized by XRD and SEM , the acidity was measured by NH3 - TPD, surface area and pore volume were determined by N2 adsorption. Toluene alkylation and o - xylene isomerization were chosen and the catalytic activity was estimated with impulse minisize reactor - chromatogram device. The results show that to luene alkylation and o - xylene isomerization convertion of nano crystalline ZSM - 5 zeolite are 60. 98 %(450 ℃) and 90. 38 %(500 ℃) respectively , which are higher than that of non - nano crystalline ZSM - 5 zeolite(46. 18% and 75. 59 %), so nano crystalline ZSM - 5 zeolite has better catalytic activity.